Amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and diffuse Lewy body (LB) disease (DLBD) are characterized by the massive degeneration of selected populations of central nervous system (CNS) neurons many of which accumulate large intraneuronal filamentous inclusions. These inclusions resemble aggregated masses of neurofilaments (NFs), and immunochemical studies implicate NF triplet proteins as the major building blocks of these abnormal filaments. In ALS, the inclusions are referred to as spheroids and they occur primarily in the proximal axons of spinal cord motor neurons. In PD and DLBD, these inclusions are termed LBs and they predominate in the perikarya of brainstem and cortical neurons. Advances in understanding the role of these NF-rich inclusions in the dysfunCtion and premature death of affected neurons have lagged behind efforts to dissect the molecular composition of these diagnostic hallmarks of ALS, PD and DLBD. To address this issue, we propose studies of transgenic mouse models of ALS to determine if spheroid-like, NF-rich inclusions in the proximal axons of spinal cord motor neurons compromise axoplasmic transport and lead to the degeneration of affected neurons. In addition, we will create transgenic mouse models that accumulate LB-like, NF-rich inclusions in CNS neurons to determine if these inclusions isolate perikaryal organelles, disrupt their functions, and lead to the death of the affected neurons. To accomplish the first objective, we will: Characterize NF pathology in transgenic mice that over-express wild type Cu/Zn superoxide dismutase (SOD1), the G93A mutant form of SOD1 as well as chimera and knock out mice that express altered levels of SOD1 in comparison with transgenic mice that express different high molecular weight NF (NFH) transgenes; Determine if NF aggregates in wild type and mutant SOD1 transgenic mice block axonal transport and lead to the degeneration of affected neurons. To accomplish the second objective, we will: Create transgenic mice with LB-like NF perikaryal aggregates in CNS neurons using cDNA constructs encoding NFH fused to LacZ or anti-sense DNA encoding gamma- glutamylcysteine synthetase driven by the tyrosine hydroxylase (TH) promoter; Determine if these mice develop LB-like, NF-rich lesions that kill neurons by entrapping cellular organelles and disrupting their normal functions. The accomplishment of these aims will clarify the role of hallmark NF lesions of ALS, PD and DLBD in the death of selected CNS neurons in these age-related neurodegenerative diseases.